This invention relates to apparatus for sensing and/or measuring changes in inclination. Such apparatus has many applications, for example in one form the apparatus may be used in the same manner and for the same purpose as a conventional spirit level. The apparatus may also be used to sense or measure small variations in tilt of a surface from a datum position, for example a truly horizontal or vertical position. Since the apparatus may also be used to measure the deflection of a structure when a load is applied thereto it may also function as a strain gauge.
It is an object of the present invention to provide an apparatus of the above kind which is simple and reliable in use but which, if desired, may also be arranged to provide a high degree of sensitivity so that very small changes in inclination may be measured with precision.
The present invention, in one aspect, consists in a sensor responsive to changes in inclination which comprises an elongated sealed chamber which is partly filled with a liquid dielectric, the remaining space being occupied by air or a gas, and a pair of electrodes associated with the chamber in such position as to lie generally one above and the other below the liquid/gas interface at a particular angle of inclination of the sensor, whereby a change in this inclination produces a corresponding change in the capacitance between the electrodes.
Conveniently the length of the upper electrode is of the order of one half the length of the lower electrode as measured in the direction of the length of the chamber, while in a preferred arrangement one end of the upper electrode is disposed approximately at the centre of the length of the lower electrode.
The present invention, in another aspect, consists in an apparatus for indicating or measuring inclination or changes in inclination comprising a sensor as above described and means for producing an indication of changes in capacitance between the electrodes of the sensor.
In one form the indication producing means may comprise a capacitance bridge having the sensor connected in one arm thereof. The bridge may be balanced for one particular inclination of the sensor and deviations from this inclination will be indicated.
In another form the indication producing means may comprise a tuned collector tuned base oscillator which operates in the region of 30 MHZ and has the sensor connected to decouple the emitter partially. In such arrangement which is sensitive to very small changes in capacitance the operating point of the transistor and hence its collector current will be proportional to the emitter decoupling capacitance, and therefore to the inclination of the sensor.